1. Field of the Invention
This invention relates to a method of producing a high quality cyclized polydiene. More particularly, the invention relates to a method of producing a cyclized polydiene suitable for use as a resinous component of a photoresist for the production of semiconductors.
2. Discussion of the Background
It has long been known that the cyclization of a polydiene such as natural rubber, synthetic polyisoprene, polybutadiene, etc. in an organic solvent gives rise to a cyclized form of the starting material polymer. Such cyclized polydienes have heretofore been used as insulating materials, adhesives, coatings, rubber compounding agents, photosensitive resins, etc. With the recent advance in integrated circuit (IC) technology, the importance of photosensitive resins for use as photoresists in the manufacture of semiconductors has been increasing. For this application, it is necessary that the cyclized polydiene have a narrow molecular weight distribution and a comparatively high degree of cyclization. Generally, when the cyclized polymer has a narrow molecular weight distribution, it gives a photoresist having a high resolution. Moreover, its degree of cyclization is preferably within the range of 40 to 75 percent, and this, together with the average molecular weight of the cyclized polymer, has a significant influence on the sensitivity of photoresist and the resist thickness remaining after development in the process of producing semiconductors.
The hitherto-known cyclization catalysts include Bronsted acids such as sulfuric acid, sulfonic acid, haloacetic acids, perchloric acid and Lewis acids such as tin tetrachloride, titanium tetrachloride, aluminum halides, boron trifluoride, organo-aluminum compounds, etc. (For example, see Rubber Age 55, 361-365 (1944) or Japanese Patent Kokai No. Sho 47-34834.)
However, since these catalysts generally are low in activity and afford only low reaction rates, they must be used in a large quantity or long reaction times are required to obtain a cyclized polydiene with a comparatively high degree of cyclization. Moreover, the resulting cyclized polydiene generally has a wide molecular weight distribution. These reactions are also low in reproducibility. Particularly when a Bronsted acid is employed, side reactions causing gelation or discoloration tend to take place. If large amounts of gels are produced, it requires a great deal of effort to separate them.
Thus, the conventional cyclization reaction cannot provide a cyclized polydiene having a narrow molecular weight distribution and a comparatively high degree of cyclization with good reproducibility and without side reactions causing gelation or discoloration.